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. . , o :J2PARTMENT OF THE ARMY OY,A}L\ D~STRICT, CORPS OF ENGINEERS O:'lARA, NEBRASKA 68102 SUPP;:::MENT TO INTERIM REPORT AND APPENDICES, BEAR CREEK, COLORADO MOUN~ CARBON RESERVOIR WITH OPTIMUM RECREATIONAL DEVELOPMENT PLAN September 1967 1, fURPOSE Following review of the Chief of Engineers' proposed report on the Bear Creek basin, Colorado, the Bureau of Outdoor Recreation recommended certain substantial modifications in the recreational aspects of the dam and reservoir project recommended by the reporting officers and concurred in by the Board of Engineers for Rivers and Harbors. This supplement presents a discussion and evaluation of the recommendations made by the Bureau of Outdoor Recreation. It summarizes the project:osts and benefits associated with such additional development, and it provides cost allocations and cost-sharing data. 2. DESCRIPrION OF PLAN OF IMPROVEMENT o a. The reporting officers recommended a plan of improvement consisti:J.g of a multip:.e-purpose dam and reservoir on Bear Creek, approximately 8 miles upstream from the confluence of Bear Creek and the South Platte Rive::', at Denver, that would provide flood protection for metropolitan Denver and the rural reaches of the South P1e.tte River &ownstream from Denver. The Division Engineer recommended, as a ~ooential maximum modification of the original plan of development} a plall essentially equivalent to the alterna- tive plac:: 5 presentao, in the basic report of the District Engineer. Recommendation of "t,he more cos1;ly alternative was based on the probability that foundation conditions unsuited to the origir.al plan might be revealed during advanced planning studi,es, wher: more detailed subsurface explorations would be undertaken. The recommended project, therefore, represeI'.ts the Claximum structure that might be required U!lder adverse foundation conditions. This would include an earthfill dam 162 feet high, with a crest length of about 4,400 feet, and a supplementaIJ' earth fill dike, with a height of 50 feet and a crest length of 2'1'00 feet, to the south of the main embankment. An earth- and rock-cut emergency spillway would be provided to insure the safety of the structure. The reservoir would prOVide storage capacity of 74,750 acre-feet, of which 2,400 acre-feet would be for sediment reserve and recreatic.n, 26,000 acre-feet would be for flood control, and 46,350 acre-feet wOc.ld be for surcharge storage. An ungated service outlet would be provided for flood control releases, and a gated low-flow outlet would be provided for release of streamflow requirements. Pertinent data for the l~commended project a~e presented in table 1. . ---- -,~